Green Leaf Volatiles

An interesting by-product of plant metabolism is the production of 'green-leaf volatiles' by oxidation of unsaturated fatty acids (Figure 3.36). These volatile compounds, which include (Z)- and (£)-3-hexenols and -3-hexenals, (£)-2-hexenal, (J£)-2-hexen-l-ol and 1-hexanol are released by some plants naturally, and especially when damaged by insects, and apparently are then sufficiently noticeable to attract parasitic wasps to the damaging insects. They are also attractive to many insects and are used by others as pheromones (aggregation in bugs) and defensive secretions (of stink bugs). A millipede secretes l-octen-3-ol, the characteristic odour of mushrooms, but what its origin is, or what protective effect it offers the millipede are not known.